1. Field of the Invention
The present invention relates to an universal multicontact connecting system fixture between an EWS probe card and a test card for a "test-on-wafer" station of a production line for semiconductor devices.
2. Description of the Prior Art
Test stations for carrying out quality control testing on wafers of integrated semiconductor devices being fabricated are installations of basic importance for controlling the quality of microelectronic productions. These tests stations are rather complex as they are equipped with sophisticated apparatuses for the automation of the testing operations in order to permit high levels of productivity in performing quality control tests on all the pieces being fabricated.
Commonly, each test station has an inventory of interchangeable EWS probe cards and an inventory of interchangeable test cards. Basically, each card is specifically constructed for testing a specific product. In particular an EWS probe card is the means by which a plurality of minute conducting probes are placed in contact with respective metal pads formed on the front surface of each integrated device being fabricated on the wafer. The electric contact between the point of each probe and the respective contact pad is established by elastic pressure and it is evident that the uniformity and reproducibility of the contact pressure are critical factors for the regularity and precision of the measurements of the electrical parameters which must be carried out on the single integrated device being fabricated. Conversely, a test card is a card which contains the appropriate circuitry for implementing predetermined biasing conditions and detecting functions of electrical parameters through the plurality of contacting probes, as well as control, compensation, and data processing functions in order to present the results of the tests in a most appropriate form to a variety of analytical equipments which determine whether the tested device fits the design specifications.
The electrical connection of the various circuital nodes of the integrated device being tested and which are contacted by means of the probes of the EWS cards, to the respective outputs and inputs of the test card are normally arranged by means of a plurality of cables, provided with end male connectors to fit female sockets present in the two cards. The cables used are often single-conductor cables. Notwithstanding the fact that these cable connections must be made when preparing the test station for testing a particular type of device, they are tedious to make and above all they are a source of problems, in consideration that the number of single-conductor cable connections may be extremely high (from 60 to 180 wires).
The cable connections between the probe card and the test card, notwithstanding the fact that they may not introduce any appreciable load asymmetry of disuniformity on the pressure held contacts established with the pads of the device on the wafer, which could severely affect the contact resistance, which for a load variation of .+-.10 gr may vary by 10-20 milliohm, still cause a problem because the reciprocal spatial disposal of the connecting cables is hardly stable and reproducible at every setting up of the station. This causes changes of capacitive and inductive couplings among signals which make necessary time consuming compensation interventions with the deployment of the RC network or with other means, which must be performed during a phase of "debugging" of the test station set-up, before the station can start functioning.
These preliminary set-up operations are time consuming and are very critical as often, an imperfect trimming may cause instability of the measurements of particularly critical parameters of the integrated device which may lead to a virtual loss of production.
Vis-a-vis this state of the art, it has been found now that these problems and drawbacks of these known fixtures, may be overcome, while greatly reducing the time necessary for setting up the test station when installing a different EWS probe card and/or a different test card in preparation for the testing of a new type of integrated device.